Magnetic nanoparticles have drawn attention as essential materials for achieving a variety of next-generation nanotechnology devices, such as high-density magnetic recording media, nanoscale electronics, radio-frequency electromagnetic wave shields, nanocomposite permanent magnets or transformer core. In the biomedical field, the magnetic nanoparticle has potential applications as novel catalysts, biomolecule labeling agents or used as contrast agent for magnetic resonance imaging (MRI). The magnetic nanoparticle further used for hyperthermia, immunological test systems, drug targeting or gene delivery. A nanocomposite permanent magnet comprising a hard magnetic phase nanoparticles and soft magnetic phase nanoparticles may have immense significance to enhance intrinsic coercivity of the permanent magnets, which may demonstrate enhanced performance at high temperatures. Magnetically soft materials with low anisotropy are advantageous in the development of read heads and in magnetic shielding applications. A steady supply of magnetic nanoparticles comprising soft magnetic phases with desirable size and magnetic properties is necessary for various applications.
Methods have been developed with primary focus to prepare nanoparticles of desired size by controlling the particle growth, however the exact details of the magnetic properties of the resulting particles are unknown. Soft magnetic nanoparticles with a high magnetic saturation are primary requirement for making a nanocomposite magnet. Thus the ability to obtain soft magnetic nanoparticles with magnetic properties approaching maximum magnetic saturation in the bulk is a desirable quality. Unlike previously reported processes on the synthesis of soft magnetic nanoparticles using iron (II) compounds and with zero valent iron precursors, a process for producing small nanoparticles, such as 5 nm to 20 nm, with magnetic saturation values approaching maximum is a long felt need.
A secondary requirement for a nanocomposite magnet is to minimize the non-magnetic material in the protective shell of the soft magnetic nanoparticle, to allow optimal coupling between the soft magnetic phase and hard magnetic phase. Methods that have been established using long chain surfactants for stabilization of small particles exhibit lower magnetic saturation (emu/g) due to ligand effects. Various attempts of heat-treatment have resulted in uncontrolled growth of the nanoparticles.
Therefore, the development of a method for synthesizing uniform nanoparticles comprising soft magnetic phases comprised of a metal or an alloy having desired particle diameter, particle size distribution, improved crystallinity, phase structure or phase purity is desired. Moreover, an economically feasible method for making magnetic nanoparticles with improved magnetic properties compared to commercially available or conventionally made magnetic nanoparticles may provide a solution for the current requirement.